Help vectors size doesn't match...why?

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cakey
cakey on 23 Oct 2014
Commented: cakey on 16 Nov 2014
This is my code to evaluate Lagrange where x_in are the given interpolation points and x_out is suppose to be f(x_in), but it keeps saying x_in and x_out don;t have the same vector length
x = -1:50;
y = 1.0 ./ (1+9*x.^2);
x_in=linspace(-1,1,100);
x_out=(1.0) ./ (1+9*(x_in).^2);
y_out=make_Ln(x,x_in,x_out);
plot(x,y,':',x_in,y_out,'*');
title('Lagrange Interpolation:x_in=linspace(-1,1,100)')
legend('y','Interpolation');
figure;
  6 Comments
cakey
cakey on 23 Oct 2014
Error using plot Vectors must be the same lengths.
cakey
cakey on 23 Oct 2014
Edited: Andrei Bobrov on 24 Oct 2014
Sorry it is this one:
y_out=make_Ln(x,x_in,x_out)
n=size(x_in,2);
L=ones(n,size(x,2));
if (size(x_in,2)~=size(x_out,2))
fprintf(1,'x_in and x_out must have same elements');
y=NaN;
else
for i=1:n
for j=1:n
if (i~=j)
L(i,:)=L(i,:).*(x-x_in(j))/(x_in(i)-x_in(j));
end
end
end
y=0;
for i=1:n
y_out=y_out+x_out(i)*L(i,:);
end
end

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Accepted Answer

Julia
Julia on 23 Oct 2014
Hi,
x_in and x_out have the same length (100).
x and y are shorter (52), but I don't know if this bothers your function make_Ln().
I suppose y_out and x_in do not match, but without knowing your function make_Ln() I cannot say more.
To plot x_in and x_out is no problem
plot(x,y,':',x_in,x_out,'*')
  7 Comments
Patrik Ek
Patrik Ek on 24 Oct 2014
Cakey i think that you should take a look at the debugger. You can easily set breakpoints in the code and check dimensions, values, etc. It is also possible to set a breakpoint if error. Both under the editor menu under breakpoints, or simply by typing dbstop error. This can be of help in the future and also to make it easier to find solutions of problems.

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